The present invention relates to an electrodeless discharge energy supply apparatus for supplying high frequency energy necessary to produce an electrodeless discharge, and an electrodeless discharge lamp apparatus using the same.
Compared with electroded arc discharge lamps, high frequency electrodeless discharge lamps have the excellent advantages that electromagnetic energy can be easily coupled to fills, that mercury can be excluded from the fills used for discharge light emission, and that high luminous efficacy is attainable. Furthermore, since there are no electrodes within discharge space, blackening of bulb inner walls due to electrode evaporation does not occur. This significantly improves lamp life. Because of these features, high frequency electrodeless discharge lamps have been researched vigorously in recent years as the next generation of discharge lamps.
Means known in the prior art for supplying high frequency energy necessary for an electrodeless discharge include a cavity resonator such as one described in Japanese Patent Unexamined Patent Publication No. Sho 59-86153.
FIG. 14 shows the construction of a prior art electrodeless discharge lamp apparatus using a cavity resonator as an electrodeless discharge energy supply apparatus, disclosed in Japanese Patent Unexamined Patent Publication No. Sho 59-86153 xe2x80x9cMicrowave Generation Type Electrodeless Lamp for Producing High Luminous Output.xe2x80x9d
The electrodeless discharge lamp 131 constructed from an optically transmissive material, such as quartz glass, filled with a discharge medium, such as a rare gas or a metal, is placed inside the cavity resonator 132 constructed from a metallic conductor. High frequency energy generated by an oscillator such as a magnetron propagates along a waveguide or the like and is coupled into the cavity resonator 132 through a high frequency coupling slot 133. A resonant standing wave occurs within the cavity resonator 132, and a discharge plasma is produced within the electrodeless discharge lamp 131 by the energy of the resonant standing wave. Light radiation emitted from the electrodeless discharge lamp is taken outside through a metallic mesh provided in an opening 134.
Since the prior art electrodeless discharge energy supply apparatus and electrodeless discharge lamp apparatus use a cavity resonator as the energy supply means, an electric field strength distribution based on the guide wavelength occurs within the cavity resonator. For example, at high frequencies of 2.45 GHz, widely used as an industrial frequency band, free space wavelength is about 12 cm. Therefore, if a discharge is produced within a discharge area wider than the half wavelength (about 6 cm) by using such a prior art apparatus, the magnitude of the electric field strength varies greatly, depending on the location within the discharge area. This has resulted in the problem that a uniform discharge cannot be obtained because of variations in discharge intensity among locations within the discharge area. The prior art apparatus such as described above has therefore not been suitable for applications such as a plane light source or a line light source that demand a uniform discharge over a wide discharge area wider than the wavelength of the applied high frequency.
There is, therefore, a need to develop an electrodeless discharge energy supply apparatus that is capable of applying a uniform electric field over a desired discharge area so that a uniform discharge can be produced over a discharge area wider than the wavelength of the applied high frequency.
In view of the above problem with the prior art energy supply apparatus, it is an object of the present invention to provide an electrodeless discharge energy supply apparatus which, compared with the prior art cavity resonator type, is capable of producing a more uniform discharge over a discharge area wider than the wavelength of the applied high frequency, and also provide an electrodeless discharge lamp apparatus using the same.
One aspect of the present invention is an electrodeless discharge energy supply apparatus comprising excitation means, having a prescribed periodic structure, for exciting a surface wave by a high frequency, wherein energy necessary to produce an electrodeless discharge is supplied using said excited surface wave.
Another aspect of the present invention is an electrodeless discharge energy supply apparatus, wherein the excitation means is a surface wave transmission line having electrical conductivity and formed in a substantially planar shape, and the surface wave supplied as the energy is a surface wave produced in the vicinity of the surface wave transmission line.
Still another aspect of the present invention is an electrodeless discharge energy supply apparatus, wherein the excitation means comprises (1) a planar substrate formed from a dielectric material and (2) a surface wave transmission line formed from a conductive material on the substrate, and wherein the surface wave supplied as the energy is a surface wave produced in the vicinity of the surface wave transmission line.
Yet another aspect of the present invention is an electrodeless discharge energy supply apparatus, wherein the excitation means is a surface wave transmission line having electrical conductivity and formed in a substantially cylindrical or semicylindrical shape, and the surface wave supplied as the energy is a surface wave produced in the vicinity of the surface wave transmission line.
With the above construction, a more uniform high frequency electric field can be applied to a planar or linear discharge space.
Still yet another aspect of the present invention is an electrodeless discharge lamp apparatus comprising: a high frequency oscillation means for generating high frequency energy; a high frequency propagation means for propagating the generated high frequency energy; an electrodeless discharge energy supply apparatus as described in any one of the present invention, a high frequency coupling means for coupling the propogated high frequency energy into the electrodeless discharge energy supply apparatus; and an electrodeless discharge lamp in which a discharge is produced by a surface wave generated by the electrodeless discharge energy supply apparatus.
With the above construction, a plane or line light source can be achieved that provides a more uniform luminance distribution over a discharge area wider than the wavelength of the applied high frequency.
The term xe2x80x9chigh frequencyxe2x80x9d in this specification refers to electromagnetic waves at frequencies of 1 MHz to 100 GHz. The present invention offers an advantageous effect particularly in microwave regions of frequencies ranging from 300 MHz to 30 GHz.